The present invention relates to a seat belt retractor for a seat belt, and more specifically to a seat belt retractor including an EA mechanism that absorbs energy of inertia applied to an occupant when movement of the occupant is restrained by the locking of the seat belt in an emergency, and a seat belt apparatus including the seat belt retractor.
A seat belt apparatus provided in a seat of a motor vehicle restrains quick movement of an occupant due to the acceleration occurring during a collision of the motor vehicle, and is a requisite apparatus aimed at the safety of the occupant's body.
The seat belt apparatus is generally composed of a seat belt (or webbing), a seat belt retractor, and a buckle device.
The retractor winds up the seat belt around a winding member (or spool), pulls the seat belt inside the retractor with a spring force, and ordinarily houses the seat belt in the condition when the seat belt is pulled inside it. When the occupant wears the seat belt, the housed seat belt is withdrawn from the retractor by pulling on a tongue plate provided at an end of the seat belt on the side opposite to the retracting-side. Then, the seat belt is worn by latching the tongue plate into the buckle device provided by the side of the seat.
In the thus constructed retractor, when a shock is applied during a collision, the seat belt is locked so as to prevent the seat belt from being withdrawn from the winding member, and the occupant's body, which is being moved quickly forward, is restrained by the locked seat belt. Currently, a pre-tensioner and a locking mechanism are generally provided to further strongly restrain the occupant's body at a time of rapid deceleration of the motor vehicle or the like.
The pre-tensioner removes the slack (or looseness) of the seat belt when an acceleration sensor detects that the motor vehicle is brought to a condition of rapid deceleration, and thereby improves the restraining force generated by the seat belt. In the pre-tensioner, there is, for example, a system where the slack of the seat belt is removed by the contraction of the entire length in a longitudinal direction of an expanding structure through the expansion of a bag-shaped body caused by the generating gas from a gas-generating device in response to a detecting signal of the acceleration sensor; a system where the slack of the seat belt is removed by the sliding of a piston inside a cylinder by the gas from a gas-generating device, thereby rotating the spool in a seat belt retracting direction via a pinion; or the like.
The locking mechanism is provided with a locking member or base that rotates together with the spool. Further, in the locking mechanism, a hooking member or pawl provided in the locking base is hooked on an inner tooth provided in a fixing side member of the motor vehicle, such as a frame of the retractor or the like, in response to the detecting signal of the acceleration sensor. Thus, a rotation of the locking base and the spool in a seat belt withdrawal direction is limited.
On the other hand, when forward movement of the occupant is quickly restrained at the time of rapid deceleration of the motor vehicle or the like as described above, an impactive force caused by the force of the restraint of the occupant's body is acted on the chest portion of the occupant or the like via the seat belt. An energy absorption mechanism (hereinafter called an “EA mechanism”) is known where a predetermined tension load of the seat belt is held while applying an unwinding resistance to the seat belt at a predetermined strength or more just after the seat belt is locked, so as to ease up the impactive force acting on the occupant, and in this condition, the seat belt is unwound within a predetermined length, and thereby the energy of the collision acting on the occupant is absorbed.
In this method, a shaft or torsion bar capable of being plastically deformed is disposed inside the spool that winds up the seat belt. One side of the torsion bar is connected to a spool side and the other side of the torsion bar is connected to a locking base side. Further, when the locking base is locked so as not to be rotatable by the locking mechanism at the time of the rapid deceleration of the motor vehicle occurring in an emergency or the like, the tension force of the seat belt restraining the occupant that moves forward by the inertia force serves as a relative rotation force in the withdrawal direction of the seat belt on one side of the torsion bar versus the other side. When the relative rotation force reaches a certain value or more, the torsion bar is plastically deformed and the energy of the collision is absorbed by the resistance of the plastic deformation at this time. Thus, regardless of the effect of the locking mechanism, the spool gradually rotates in the seat belt withdrawal direction, the seat belt is unwound while receiving the tension force of a certain value or more, and the force acting between the seat belt and the occupant's body is lessened.
For example, the seat belt retractor in Japanese Unexamined Patent Application Publication No. 2002-120693, is provided with a pre-tensioner connected with the spool in a rotating connection, a locking mechanism, and an EA mechanism as described above. When a slight rotation of the spool in the seat belt withdrawal direction is allowed during the operation of the EA mechanism, the pre-tensioner is already operating in the seat belt retracting direction (namely, in a reverse direction).
However, in the aforementioned known technology, the below problem exists. In the situation in which one side of the torsion bar in a spool is connected to a pre-tensioner, and a locking base to be locked by a locking mechanism is connected to the other side of the torsion bar, and when the locking mechanism locks the rotation in the retracting direction of the other side of the torsion bar after the pre-tensioner is operated in the retracting direction of the spool, and when the one side of the torsion bar performs a relative rotation while being twisted against the other side by an EA mechanism, an operation of the pre-tensioner is performed in the reverse direction to the direction of the relative rotation thereof, and the operation of the pre-tensioner blocks the relative rotation. The operation of the EA mechanism receives an influence of the operation of the pre-tensioner. This situation results in it being difficult to secure a stable operation.